The synthesis of polybenzimidazole-based, high-performance fibers requires the selective polymerization of 1,2,4,5-tetraminobenzene (“TAB”) with various substituted and unsubstituted aromatic diacids, such as 2,5-dihydroxyterephthalic acid (“DHTA”).
TAB may be prepared, for example, starting with m-phenylenediamine as described by Ruggli and Fischer in Helvetica Chimica Acta (1945), 28, 1270-80. TAB has also been synthesized, for example, from dinitrodiaminobenzene via reduction. Various known reduction processes use stoichiometric amounts of Sn in HCl, or Pd/C, as catalysts for the hydrogenation in high boiling diglyme, and in the presence of stoichiometric amounts of trifluoromethane sulfonic acid. These processes have high costs associated with reagents, waste management, and solvent usage. They also require several workup and purification steps. In addition, safety concerns exist, especially with respect to the sensitizing properties of some intermediates. For reasons of cost and safety, it would be desirable to have a process for making TAB where intermediates do not need to be isolated as dry materials.
Moreover, once TAB has been prepared, the oxidative instability of various TAB species, including TAB, TAB salts such as TAB.nHX (n=0-4, X=Cl, Br), and a complex of TAB with an aromatic diacid, leads to the formation of oxidation byproducts, such as 3,6-diiminocyclohexa-1,4-diene-1,4-diamine, as represented by the structure of the following Formula (II)
and phenazine-2,3,7,8-tetraamine, as represented by the structure of the following Formula (III):
by mechanisms such as the following:

There thus remains a need for an improved process for the safe and efficient production of high-purity 1,2,4,5-tetraminobenzene and derivatives thereof in a manner that avoids the presence of oxidation byproducts and contamination with reducing agents.